My favorite use of .. so far is:

# From the "LIBFILES =" line to the first line that 
# doesn't end in a backslash,                       
# collect library directory names                   
if (my $status = s/^\s*LIBFILES\s*=// .. !s/\\$//) {
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which matches the lines I wanted in a Makefile while simultaneously removing what I didn't want (the 'LIBFILES=' section prefix and the backslash continuation marker) from the lines.